Semiconductor optical devices (SODs), such as laser diodes and light-emitting diodes, are currently found in a wide variety of applications including consumer electronics and fiber optic communication systems. Nevertheless, in many applications, the implementation of SODs is made significantly more complex by the fact that an SOD's operating characteristics will vary considerably with temperature. For example, emission wavelength, threshold current and operating lifetimes of laser diodes are all strong functions of temperature. For a typical laser diode generating 3 mW of light output at a wavelength of 780 nm, the wavelength will shift an average of 0.26 nm/° C. and the threshold current will shift an average of 0.3 mA/° C. In addition, the operating lifetime drops by a factor of two for every 25° C. rise in operating temperature.
Thermoelectric coolers (TECs) are a type of active cooling device that provide a simple and reliable solution to precise temperature control in many applications involving SODs. A TEC may, for example, be capable of heating or cooling a small thermal load such as a laser diode by greater than 60° C. from ambient temperature, while at the same time achieving temperature stabilities of better than 0.001° C. A TEC typically comprises a cold thermally conductive plate and a hot thermally conductive plate. In order to regulate the temperature of an SOD, the SOD is placed in thermal contact with the cold thermally conductive plate, usually via a thermally conductive material like copper. Within the TEC, heat is transferred from the cold thermally conductive plate to the hot thermally conductive plate by passing current through dozens of thermoelectric cooling couples that span the space between the thermally conductive plates. Each of the thermoelectric cooling couples, in turn, comprises two heavily doped semiconductor blocks (usually formed of bismuth telluride) which are connected electrically in series. In this configuration, the rate of heat transfer from the cold thermally conductive plate to the hot thermally conductive plate is typically proportional to the current passing through the thermoelectric cooling couples and the number of thermoelectric cooling couples forming the TEC.
Unfortunately, however, every active cooling device such as a TEC adds to the cost of implementing an SOD while at the same time consuming valuable space within the electronic apparatus containing the SOD. Moreover, these detrimental aspects are further amplified in modern electronic apparatus comprising more than one SOD. Such multi-SOD electronic apparatus may include, for example, optical storage drives comprising multiple laser diodes capable of handling some combination of compact disc (CD), digital versatile disc (DVD), Blu-Ray and high definition DVD (HD-DVD) optical disc formats. Conventionally, each laser diode in such an application would require its own active cooling device.
As a result, there is a need for an optical assembly comprising multiple SODs wherein temperature regulation is provided by just a single active cooling device.